1. Field of the Invention
This invention relates to a method of making a hollow, stretch blown plastic container, and to the resulting product, such as a bottle, with a relatively large size as compared to the size of the opening in the container.
2. Brief Description of the Prior Art
Plastic containers, that is, containers constructed primarily of substituted or unsubstituted hydrocarbons have, for some time, been in prevalent use. Increased popularity, as compared with inorganic glass, the increased popularity of such plastic containers is due to a variety of factors in particular improved impact resistance, reduced weight, and, perhaps most significantly, reduced cost.
As would be expected, procedures for producing so popular a commodity have been in continuing transition. What started as a simple operation, analogous to that used for inorganic glass has evolved through a variety of stages. Today, most containers are produced by procedures which involve the initial formation of a preform, sometimes denoted a parison, followed by expansion of the preform to produce the final containers. Preforms are commonly produced by any of the various molding operations with extrusion and injection being predominant methods. The term xe2x80x9cpreformxe2x80x9d generally indicates a solid article produced by injection molding, extrusion, or the like, which is removed from the mold in which it is formed and subsequently transferred to a blow mold where it is expanded to a final shape. The term xe2x80x9cparisonxe2x80x9d is sometimes used for such objects, although it more properly refers to an extruded mass of plastic that is immediately blow molded without undergoing an intermediate solidification. In this application, the term xe2x80x9cpreformxe2x80x9d is used to denote a solid molded intermediate article which is subsequently heated and expanded in a blow mold to form a final shaped article, and is intended to include the term xe2x80x9cparisonxe2x80x9d if that term is used to denote such an intermediate article. Expansion of the preform is commonly carried out by means of internal gas pressure with the final form of the container being determined by a mold specifically designed for this operation.
A most sophisticated form of blow molding is now commercially significant. It differs from earlier procedures in that the preform is first stretched and then blown while its temperature is much lower than with conventional processesxe2x80x94generally, within the 100xc2x0 F. range above Tc; (the temperature at which the plastic material passes from the glass phase to the rubber phase). This procedure, which is known as stretchblow molding, or orientation blow molding, is not only replacing more conventional procedures, but has opened new markets. Advantages of the procedures are all related to biaxial orientation of the polymer material. Regardless of how the preform is initially formed, e.g., whether by extrusion or injection, and regardless of whether the procedure is two-stage or in-line, the preform, while at a temperature insufficient to permit free plastic flow is expanded biaxially to conform with the blow mold. The temperature of operation, generally within the 100xc2x0 F. range immediately above Tc, is such that the expansion introduces true strain into the material. When translated into a definable polymer orientation the strain results in a number of positive attributes. Alignment of the polymeric molecules results in increased tensile strength, as well as increased-clarity,increased impact strength, and reduced creep.
A vast market for carbonated soft drink containers is a direct result of significantly improved gas barrier properties Suitable container materials are substituted and unsubstituted thermoplastic hydrocarbons. Commonly used materials at this time include polyethylene terephthalate, and polypropylene. The procedures described above are well known and included in standard reference texts. See, for example, Modern Plastics Encyclopedia, Vol. 54, No. 10A, 1977-1978, McGraw-Hill Publishing Co. (e.g., sections on xe2x80x9cBlow Moldingxe2x80x9d at page 230 et seq.; xe2x80x9cInjection-Blow Moldingxe2x80x9d at page 232 et seq.; and xe2x80x9cStretch-blow Moldingxe2x80x9d at page 233 et seq.).
It is well known that the various types of stretch-blow molding procedures have not been successful in producing containers with a large size relative to the size of the opening in the container. Yet there is a commercial demand for clear containers with such a large size relative to the size of the opening in the container, especially when used to contain water, juice, and other non-carbonated beverages. The small opening size is desirable so that relatively small size closures or dispensing valves can be used.
The problem with producing large size containers relative to the size of the opening in the container is that the extent to which the plastic can be stretched to increase the interior diameter of the preform to the interior size of the container has a practical limit. The interior diameter of the preform (see FIG. 1) is limited to the diameter of the opening in the container.
A preform with a larger interior diameter in the body than in the opening (such as illustrated in FIG. 2) would allow manufacture of relatively large containers with a small opening. However, a preform such as shown in FIG. 2 cannot be injection molded (as most preforms are for the stretch blow process) since a mold core with a diameter large enough to form the inside diameter of the preform body cannot be removed through the small opening.
Accordingly a need has continued to exist for a method of manufacturing a large-diameter blow-molded plastic container having a relatively narrow mouth.
The present invention is directed to a method for producing a preform with a large interior diameter body and small interior diameter opening (as shown in FIG. 2 of the drawings.) To accomplish this result the preform is injection molded in two parts (as in FIG. 3) so that the core can be removed from the interior of the large body of the preform.
The two parts are then joined together (as shown in FIG. 4) using any conventional method including, for example, spin welding, hot plate welding, ultrasonic welding, solvent welding, cementing, laser welding, mechanical joining, or the like. The joined preform is then used to stretch blow a container that is larger than current methods can produce with the same opening (see FIG. 5 for example.)